1. Field of the Invention
The present invention relates generally to a composite electric part of a stacked multi-layer structure, and more particularly to an electric part of a composite structure which incorporates coils and capacitors implemented in a stacked or laminated multi-layer configuration.
2. Description of the Prior Art
In manufacturing of a composite electric part of the stacked multi-layer structure type mentioned above, the capacitor layers can be realized in an integrated structure relatively easily by resorting to a stacked-layer capacitor manufacturing technique known heretofore. However, difficulty is often encountered in implementing the coil layers in an integrally stacked structure. The techniques which can be utilized to this end are limited, although several proposals have heretobefore been made, as typified by the one disclosed in Japanese Patent Publication No. 39521/1982.
According to the technique disclosed in the abovementioned publication, magnetic layers of a ferrite material and electric conductors constituting a coil are stacked alternately by employing a printing process, which is then followed by sintering the stacked layer structure thus formed at a high temperature. In practice, for implementing the stacked layer structure, such a method is commonly adopted which comprises a step of forming by printing a film conductor of a length corresponding to about a half-turn of the coil on a substrate, a step of applying a magnetic film thereon with end portions of the conductor being exposed, and a step of printing a film conductor corresponding to the remaining half-turn on the magnetic layer in such manner that an electric connection is made to the first mentioned conductor. The steps mentioned above are repeated until a coil having a desired number of turns has been realized, whereby the coil structure composed of a magnetic material and windings wound helically in the stacking direction at a predetermined pitch is formed. By sintering the stacked layer structure thus formed, there can be obtained an integrated multi-layer coil structure incorporating the coil embedded or buried in the magnetic material at a high integration density. By integrating the stacked layer coil with a capacitor of a stacked layer structure manufactured through a similar process, there can finally be realized a composite electric part of a stacked layer structure in a miniature size with a high integration density and capable of exhibiting high performance.
The composite electric part of the stacked multi-layer structure (hereinafter also referred to simply as the multi-layer composite electric part) finds a variety of numerous applications such as for implementations of trap elements, low-pass filters, high-pass filters, band-pass filters, equalizers, IFTs and the like. Accordingly, values of capacitance and inductance of the multi-layer composite electric part as well as network configuration of the capacitors and the coils has to be susceptible to selection over a wide range. In this connection, it is noted that the value and the network configuration of the capacitor can easily be adjusted over a wide range by selecting appropriately the number of the stacked layers, the number of electrodes or plates, manner of interconnection and other factors.
In contrast, in the case of an inductor structure manufactured by the layer stacking method disclosed in, for example, Japanese Patent Publication No. 39521/1982, the value of inductance is necessarily determined in dependence on the number of the stacked layers because of the three-dimensional structure is which the coil conductors are disposed in continuation to one another in the directions in which the layers are stacked. Accordingly, for selecting the inductance value or more particularly for increasing that value, the number of the layers has to be increased correspondingly. Consequently, as the inductance value increases, the number of the layers to be stacked is also increased correspondingly, which results in an increased overall thickness of the stacked coil structure in contradiction to the demand for a miniaturized thin structure.
In conjuction with the selective determination of the inductance value, it is conceivable to form a plurality of coil conductors individually, wherein the conductors are connected in series exteriorly of the coil structure. In that case, however, the sectional area occupied by one coil will be increased, resulting in a correspondingly enlarged size.
As another example of the stacked layer coil, there has also been proposed such a coil structure in which a plurality of individual spiral coil conductors wound with a pitch in a same direction are embedded in axial juxtaposition within a body of a magnetic material. With such coil structure, however, the leading end and the trailing end of each of the plural coil conductors are disposed in the same direction. By way of example, when the leading end of each coil conductor assumes a position beneath the magnetic layer, then the trailing end thereof is positioned on the top thereof. Accordingly, for connecting the coil conductors such that magnetic fields are generated in a same direction, the trailing end of the coil conductor located at the top of the magnetic layer has to be led out and connected to the leading end of the other coil conductor located at the bottom. It is however impossible to realize such electric connection interiorly of the magnetic material. It is indispensably required to lead out the leading and trailing ends of the top and bottom coil conductors exteriorly of the magnetic material and connect them by using external terminals or the like. Consequently, interconnection of the individual coil conductors requires much complicated procedure, involving an increased number of manufacturing steps, not to say of undesirableness from the viewpoint of the characteristics of the coil.